Conventionally, a filter material storage device is arranged in the gas passage system for filtering. But the filter material itself will gradually become ineffective during the filtration of air and needs to be treated before reuse, or removed and replaced with new filter material. Thus, the filter material is used as a consumable, a large consumption of which will thereby lead to not only an increase in the cost but inconvenience for users during operation and maintenance.
To solve the above problems, some compromising solutions are provided, such as a method of using a filter material that can be regenerated automatically, wherein a reusable filter material is used and in case of getting ineffective, cleaned by thermal treatment within the instrument and reused after the recovery of its function without the need for replacement. The benefits of these methods reside in their capability to avoid replacing the filter material, however, a complicated gas passage system is usually necessary, and the power consumption for heating is relatively high.